Where is the line drawn between politics and entertainment? In the final instalment of the excellent second series of Charlie Brooker's Black Mirror, that issue is exactly what is under the spotlight. It's perhaps the most plausible episode of the show so far, following what happens when a cartoon bear (presenting a particularly juvenile but popular brand of humour) ends up participating as a candidate in a by-election.

The blue bear, named Waldo, is voiced by young comedian Jaime (Daniel Rigby) and provides audiences with empty amusement by vulgarly pointing fun at politicians. Sensing the character's potential, Jack Napier (Jason Flemyng) pushes for Waldo to get his own pilot. Things take an unexpected turn, however, when a brainstorming session leads to the idea of running Waldo against the real politicians as a joke.

It's a situation that's just about ridiculous enough to be believable, and I wonder just how many voters would ironically support a cartoon if there were an opportunity to do so. As with any episode of Black Mirror, the story here explores a whole range of topical issues. Mostly focussed on cynicism felt towards politicians, it touches on how much we trust those that make the decisions, how closely aligned the election process and entertainment are and how greatly the public can be influenced by the media.

More openly comedic and satirical than the other two episodes in the series, "The Waldo Moment" approaches its material in a confident manner. The performances are effective throughout, as Rigby particularly impresses with his portrayal of the central disillusioned comedian. Chloe Pirrie is also notable as Labour candidate Gwendolyn Harris, a young woman more interested in her career than being responsible for any real changes.

Brooker's script sharply satirises the emptiness of modern politics, as the increasingly conflicted Jamie eventually strikes out angrily against the system. The true message echoes in what is possibly the episode's strongest line, though, when Conservative candidate Liam Monroe (Tobias Menzies) bleakly makes an observation about the prospect of facing Waldo. "If that thing is the main opposition then the whole system looks absurd," he says, "which it may well be - but it built these roads."

This is an episode that points out the flaws in a political system while it also concludes that cynicism and apathy lead nowhere. If there's any main target of the satire here it is the uninformed masses. They'll happily vote for Waldo because he's a funny character and they've had enough of conventional politicians. It's hardly a positive depiction of the general public but it seems a fitting one.

The second series of Black Mirror has been even more assured and complex than the first was, and both are equally important. Blending thoughtful drama and intelligent comedy is no simple task, and this concluding episode brings the series to a memorable ending. While it isn't as subtle or nuanced as the other offerings, this episode is a compelling and unsettlingly realistic depiction of the present state of politics.